AbstractA forced-flow NbTi superconducting helical coil was fabricated as research and development of the helical coil for the Large Helical Device (LHD), corresponding to a 14 scale model of the LHD. A computer-controlled helical-winding machine employing the roller bending method with twisting capability was also developed. The maximum assembly error of the conductors decreased to about 0.7 mm by optimal control of the winding curvature and torsion of the conductors. Three-dimensional structural analysis of the helical coil and the support structure was carried out to assess the mechanical integrity of the coil and support structure and to understand their mechanical behavior under the electromagnetic force. Analytical results show that the coil support structure can keep the maximum deformation of the conductors less than .4 mm, which corresponds to the required field accuracy of 5 × 10−4.